The present invention relates to an irrigating cannula for extracting the lens nucleus for use in extracapsular cataract extraction.
The lens is composed of lens cortex and lens nucleus which are made of lens fibers and fill up the lens capsule. The epithelium of the lens proliferates with age, and old epithelial cells collect in the center of the lens and become compressed, forming a lens nucleus of opaque sol in the form of a lens 6 to 9 mm in diameter. When opacities are formed in the path for light rays entering the pupil and travelling through the lens cortex and lens nucleus, serious visual impairment results which is a disease called a cataract.
The cataract is treated by removing the opaque lens and correcting the vision with a spectacle lens or contact lens or inserting an artificial lens as a substitute. The methods of removing the lens include intracapsular cataract extraction wherein the lens is entirely removed, and extracapsular cataract extraction wherein the anterior lens capsule, lens cortex and lens nucleus are removed with the posterior lens capsule only left unremoved.
Although inracapsular extraction was performed formally, extracapsular extraction is the primary practice in recent years for various reasons.
The present invention provides an irrigating cannula for removing the lens nucleus by extracapsular cataract extraction.
To remove the lens nucleus by extracapsular extraction, it has heretofore been practice to make an incision in the cornea, remove the anterior lens capsule and force out the lens nucleus from the lens cortex by applying pressure to the eyeball while lifting the cornea in accordance with the condition. With this method, the ophthalmologist and his assistant require skill in forcing out the lens nucleus smoothly. Moreover, since the lens nucleus is pushed out in frictional contact with the rear surface of the cornea by the pressure applied to the eyeball, there is a great likelihood that the cornea will be injured on the rear side.
As other methods, it is also known to directly scoop up the lens nucleus with a lens loop while dividing the lens cortex, or to directly contact a cryoprobe with the lens nucleus and withdraw the nucleus through a divided portion of the lens cortex, but because the lens cortex is a highly viscous gel, it is technically difficult to handle the lens nucleus or to attach the cryoprobe to the nucleus while dividing the lens cortex.
Especially if inserted through the lens cortex to an improper depth, the lens loop is likely to injure the posterior lens capsule by contact therewith.